But Birmingham, with four draws and a defeat from their previous five league games, were on top for the remainder of the first half.

Andrew Shinnie saw a long-range effort saved by Konstantopoulos, while Donaldson was a constant threat.

And it was Donaldson's pace in getting first to a poor back pass from Ben Gibson that saw him knock the ball past Konstantopoulos before being tripped by the Boro keeper, who was shown the red card.

Replacement Tomas Mejias, who came on for striker Jelle Vossen, was unable to keep out the penalty from Caddis as Birmingham led at the break.

But former Boro full-back Jonathan Grounds and winger David Cotterill missed chances early in the second half.

And the visitors then built up some pressure, earning their reward when the impressive Grant Leadbitter slipped through a pass from the edge of the penalty area for Bamford to calmly slot a low shot past Randolph.

That gave Boro the result they needed to head the promotion race, although they were almost denied in stoppage time when Donaldson headed a Caddis cross over the bar from six yards out.

Middlesbrough manager Aitor Karanka told his club's website:

"I'm very proud of all the players. They know that and I told them after the game that finally we're at the top of the table and we are there because all of them deserve it.

"After 31 games we're at the top and I don't know if anyone thought we would be in this position back in June or July.

"Now we have to defend this position and it's going to be very difficult. This league will be tight until the end.

"We're top of the table but we will be making a mistake thinking everything is done. All the players are doing really well so we have to enjoy being in this position and defend it now."

Birmingham manager Gary Rowett: "Had you of asked me before the game would I be pleased with a point I would have said of course but after Middlesbrough going down to 10-men and being 1-0 up I am disappointed we did not take all three points.

"As for off the field concerns, and the potential deduction of 10 points,

"I can't control that and I said that to the players. Off the pitch we can't control what happens.

"The news the days before the game I just think it spread a bit of negativity among the staff and the players initially.

"But if it needs to be done to move the club forward so be it. We just have to concentrate on what we do.

"If the worst comes to the worst and we lose 10 points, which I don't think it will, we will crack on. I don't think it will come to that. I think the club is financially stable."

Middlesbrough goalkeeper Dimi Konstantopoulos is sent off by referee David Coote to leave his side with 10 men for more than 45 minutes

Birmingham defender Paul Caddis scored his sixth goal of the season to give the Blues the lead